Improving fuel economy is an important aspect of formulating a motor oil. It is known that the fuel efficiency of an engine oil can be improved by using friction reducing additives. It is known that these additives must be active at engine operational temperature in order to be most effective.
Zinc dialkyldithiophosphates (ZDDPs) have been used as anti-fatigue, anti-wear, extreme pressure and friction modifying additives for lubricating oils for many years. However, they are subject to several drawbacks owing to their zinc and phosphorus contents. During operation of an internal combustion engine, lubricating oil enters the combustion chambers by means such as clinging to cylinder walls as the piston makes its down stroke. When phosphorus-containing lubricating oil compositions enter the combustion reaction, phosphorus enters the exhaust stream where it acts as a catalyst poison thus shortening the useful life of the catalytic converter. In addition, the presence of zinc contributes to the emission of particulates in the exhaust.
In view of the aforementioned shortcomings with the known zinc and phosphorus-containing additives, efforts have been made to provide lubricating oil additives which contain neither zinc nor phosphorus. Illustrative of non-zinc (i.e., ashless), non-phosphorus-containing lubricating oil additives are the reaction products of 2,5-dimercapto-1,3,4-thiadiazole and unsaturated mono-, di- and tri-glycerides of U.S. Pat. No. 5,512,190 and the dialkyl dithiocarbamate-derived organic ethers of U.S. Pat. No. 5,514,189.
Certain molybdenum dithiocarbamates are known as useful as lubricant additives. For example, U.S. Pat. No. 3,356,702 describes certain molybdenum oxysulfate dithiocarbamates useful as extreme pressure agent, antioxidant and wear inhibitor for lubricants. U.S. Pat. No. 4,098,705 describes certain sulfur containing molybdenum dihydrocarbyldithiocarbamates useful as lubricant additives. U.S. Pat. No. 4,178,258 describes lubricating oil compositions comprising certain molybdenum bis(dialkyldithiocarbamates).
It a purpose of this invention to provide novel dithiocarbamyl carboxylic acid and amide compounds useful as lubricant additives. It is also a purpose of this invention to provide novel additives for lubricating oils that can improve the friction reducing properties of the oils.